Sphingosine-1-phosphate (S1P) has been demonstrated to induce many cellular effects, including those that result in platelet aggregation, cell proliferation, cell morphology changes, tumor cell invasion, endothelial cell chemotaxis and endothelial cell in vitro angiogenesis. S1P receptors are therefore good targets for therapeutic applications such as wound healing and tumor growth inhibition. S1P signals cells in part via a set of G protein-coupled receptors named S1P1, S1P2, S1P3, S1P4, and S1P5 (formerly called EDG-1, EDG-5, EDG-3, EDG-6, and EDG-8, respectively). These receptors share 50-55% amino acid and cluster identity with three other receptors (LPA1, LPA2, and LPA3 (formerly EDG-2, EDG-4 and EDG-7)) for the structurally-related lysophosphatidic acid (LPA).
A conformational shift is induced in the G-Protein Coupled Receptor (GPCR) when the ligand binds to that receptor, causing GDP to be replaced by GTP on the α-subunit of the associated G-proteins and subsequent release of the G-proteins into the cytoplasm. The α-subunit then dissociates from the βγ-subunit, and each subunit can then associate with effector proteins, which activate second messengers leading to a cellular response. Eventually the GTP on the G-proteins is hydrolyzed to GDP, and the subunits of the G-proteins re-associate with each other and then with the receptor. Amplification plays a major role in the general GPCR pathway. The binding of one ligand to one receptor leads to the activation of many G-proteins, each capable of associating with many effector proteins, leading to an amplified cellular response.
S1P receptors make good drug targets, because individual receptors are both tissue- and response-specific. Tissue specificity of the S1P receptors is important, because development of an agonist or antagonist selective for one receptor localizes the cellular response to tissues containing that receptor, limiting unwanted side effects. Response specificity of the S1P receptors is also important because it allows for development of agonists or antagonists that initiate or suppress certain cellular responses without affecting other things.
For example, the S1P1 receptor subtype plays a key role in lymphocyte trafficking, and it is well established that synthetic small molecule S1P1 receptor agonists can suppress the peripheral immune response by inducing lymphocyte sequestration in secondary lymph organs (Cooke, N.; Zecri, F. Sphingosine 1-phosphate type 1 receptor modulators: recent advances and therapeutic potential. Ann. Reports Med. Chem. 2007; 42: 245-263).
Identification of the importance of this axis in modulating immune function was primarily accomplished via reverse pharmacology with the small molecule FTY720 (fingolimod). FTY720 is a prodrug that is phosphorylated in vivo to generate FTY720-P, an agonist of all known S1P receptors with the exception of S1P2 (Mandala S, Hajdu R, Bergstrom J, et al. Alteration of lymphocyte trafficking by sphingosine-1-phosphate receptor agonists. Science. 2002; 296:346-349). Preclinical studies established that FTY720 administration resulted in peripheral lymphopenia that was associated with beneficial outcomes in animal models of transplantation (Brinkmann V and Lynch K. R. FTY720: targeting G-protein-coupled receptors for spingosine-1-phosphate in transplantation and autoimmunity. Curr. Op. Immunol. 2002; 14:569-575 and references therein) and autoimmune diseases (e.g. arthritis; Matsuura M, Imayoshi T and Okumoto T. Effect of FTY720, a novel immunosuppressant, on adjuvant- and collagen-induced arthritis in rats. Int. J of Immunopharm. 2000; 22:323-331), including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS); (Kataoka H, Sugahara K, Shimano K, et al. FTY720, sphingosine 1-phosphate receptor modulator, ameliorates experimental autoimmune encephalomyelitis by inhibition of T cell infiltration. Cell. and Mol. Immunol. 2005; 2(6):439-448; MRL-lpr/lpr mice, an animal model of systemic lupus erythematosus (SLE) (Okazaki H, Hirata D, Kamimura T et al. Effects of FTY720 in MRL-lpr/lpr Mice: Therapeutic Potential in Systemic Lupus Erythematosus. J. Rheumatol. 2002; 29:707-716) and development of diabetes in NOD mice (Yang Z., Chen M. Fialkow L B et al. Immune modulator FTY720 prevents autoimmune diabetes in non obese diabetic mice. Clin Immunol. 2003; 107:30-35). In addition, results from a recently completed clinical trial of FTY720 (Phase 2) in MS patients highlight the potential of S1P receptor agonism as an effective therapeutic approach for treating human autoimmune diseases (Kappos L, Antel J, Comi G, et al. Oral fingolimod (FTY720) for relapsing multiple sclerosis. N Engl. J. Med. 2006; 355(11):1124-1140).
The current therapies for the treatment of immune diseases usually suppress the whole immune system of the patient and hence the bodys ability to react to infections is also severely compromised. Typical drugs in this class include azathioprine, chlorambucil, cyclophosphamide, cyclosporin, or methotrexate. Corticosteroids which reduce inflammation and suppress the immune response, cause side effects when used in long term treatment. Nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce pain and inflammation, however, they exhibit considerable side effects such as gastrointestinal bleeding. Accordingly, there is a need for treatments that do not suffer from these side effects. The present invention fulfills this and related needs.